A variety of methods for transmitting high-quality and high-volume data using limited radio resources has been appeared in the current wireless communication systems. In addition, a closed-loop system for providing a feedback channel from a user equipment to a base station is spotlighted as a means for improving system performance.
If the user equipment provides channel information to the base station, the base station adjusts a variety of system parameters, such as a power level, transmission format, and the like, using the provided channel information to maximize the system performance. For example, an adaptive modulation and coding (AMC) technique is a technique performed by the base station to enhance link performance by adjusting a modulation and coding scheme using feedback channel information. If channel status is favorable, a data transmission rate is increased, whereas if the channel is degraded, the data transmission rate is decreased, thereby supporting efficient transmission and increasing an average transmission rate as a result.
Hereinafter, a downlink means a communication from the base station to the user equipment, and an uplink means a communication from the user equipment to the base station.
In order to efficiently transmit downlink data from the base station to the user equipment, the base station needs to allocate best resources to each user equipment. In order to allow the base station to allocate appropriate resources to the user equipment, channel quality information (hereinafter, referred to as a CQI) is needed.
Generally, a CQI is measured at the user equipment and fed back from the user equipment to the base station through an uplink channel. However, overheads are frequently occurred by the feedback of the CQI. Particularly, in a system using multiple carriers, such as an orthogonal frequency division multiplexing (OFDM) system, since a CQI of each carrier can be different from those of the others, the user equipment transmits a CQI for each carrier. However, in this case, feedback of CQIs may invite waste of uplink resources and decreases uplink capacity as a result.
Accordingly, a method of efficiently transmitting CQIs while reducing overheads incurred by CQI feedback is required.